Here's how Marshall describes the test:
Is it representative of the rest of the book? Would a reader skimming that page be inclined to read on? The fact is, p 69 may well not be representative of the book, but the answer gives you an opportunity to say something about what your book really is about and how that page fits in or ... whatever you like.
He has over 160 books tested so far.
How could I resist that offer?? It was an interesting and difficult experience. It felt a little like an English composition assignment, but it was fun, too.
Check out the Page 69 Test for Shooting Gallery. How does your other favorite book fare?